Chapter 24
Section 1 The Digestive System
Digestive System at a Glance
• Your digestive system is a group of organs that
break down food so that it can be used by the body.
• Food passes through the digestive tract. The
digestive tract includes your mouth, pharynx,
esophagus, stomach, small intestine, large intestine,
rectum, and anus.
• The liver, gallbladder, pancreas, and salivary glands
are also part of the digestive system.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Breaking Down Food
• The breaking, crushing, and mashing
of food is called mechanical digestion.
• In chemical digestion, large
molecules are broken down into
nutrients with the aid of enzymes.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Digestion Begins in the Mouth
• Teeth - With the help
of strong jaw muscles,
teeth break and grind
food.
•Incisors - shred/cut
•Canines – shred/tear
•Pre-molars – mash
•Molars - grind
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Digestion Begins in the Mouth, continued
Saliva contains an enzyme that
begins the chemical digestion of
carbohydrates (sugars).
•
•Taste Buds – Nerve centers on the
tongue that detect sweet, sour,
bitter, and salty flavors.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Digestion Begins in the Mouth, continued
•Leaving the Mouth Once the food has been
reduced to a soft mush, the tongue pushes it
into the throat, which leads to a long, straight,
slippery tube called the esophagus. The
esophagus is about 25 cm long and food
travels down it due to gravity and peristalsis
(wave of rhythmic muscle contractions that
push the food through the tube)
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The Harsh Environment of the Stomach
• The stomach is a muscular, saclike, digestive organ
attached to the lower end of the esophagus.
• Tiny glands in the stomach produce enzymes and
acid (HCl) to break food down into nutrients.
• After a few hours of combined mechanical and
chemical digestion, food leaves your stomach as a
soupy mixture called chyme.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The Pancreas and Small Intestine
• The Pancreas is an organ located between the
stomach and small intestine. Its makes pancreatic
fluids that protect the small intestine from the acid in
chyme and releases insulin to help regulate blood
sugar.
• The Small Intestine is a muscular tube that is 2.5 cm
in diameter, but about 6 meters (20 ft) long! In the
small intestine, nutrients are absorbed into the
bloodstream through fingerlike projections called villi.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The Liver and the Gallbladder
• The liver is a large, reddish brown organ that helps
with digestion by making bile to break up fat.
• Bile is stored in a saclike organ called the
gallbladder, which squeezes the bile into the small
intestine.
• The liver also stores excess nutrients until the body
is ready to absorb them into the bloodstream.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The Liver and the Gallbladder, continued
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The End of the Line
• Material that can’t be absorbed into the blood is
pushed into the large intestine.
• The large intestine is a horseshoe-shaped tube that
is 6.5 cm in diameter and about 1.5 meters long. It
absorbs most of the water in undigested material and
changes the liquid into semisolid waste material
called feces, or stool.
• Feces are stored in the rectum until they can be
expelled.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 24
Section 1 The Digestive System
The End of the Line, continued
• Feces pass to the
outside of the body
through an opening
called the anus.
• It has taken each of
your meals about 24
hours to make this
journey through your
digestive system.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.